To determine whether the effect of myostatin deletion on adipose tissue size is direct or indirect, we have made a transgenic line of mice that does not have myostatin signaling in fat cells. We have characterized the body composition, insulin sensitivity, and resistance to high fat diet of these mice. We have compared the metabolism of this line to mice that do not have myostatin signaling specifically in skeletal muscle and to mice with a global deletion of myostatin. We have also analyzed the effects of exercise on myostatin mull mice as compared to wild type mice.